Death from the complications of truncal hemorrhage continues to exist as a high probability in an overwhelming number of cases in both the military and civilian medical spheres. Existing systems and procedures used to control truncal hemorrhage frequently contribute to a patient's ultimate death through inability to maintain adequate blood flow to vital organs. It is well recognized that without controlled distal reperfusion, hemodynamic collapse is common, particularly where open aortic cross-clamping is used to stop hemorrhage. The ability to rapidly deliver effective, variable, and adaptive control of aortic flow for hemorrhaging patients will save innumerable lives.
Mitigation of battlefield injury and hemorrhage is a high priority of U.S. military trauma surgeons and researchers. Uncontrolled blood loss is recognized as the leading cause of death in 90 percent of the potentially survivable battlefield cases and in 80 percent of those who died in a military treatment facility. “Bleed-outs,” especially those caused by groin or neck wounds, challenge medics, corpsmen and physicians who can do little to stop blood loss caused by major arterial injuries.
Two devices, the Combat Ready Clamp and Abdominal Aortic Tourniquet, have been built to treat truncal injuries. The Combat Ready Clamp is primarily for treating junctional hemorrhage (i.e. between the trunk and an extremity). The Combat Ready Clamp is ineffective against wounds involving the genital region or the loss of both legs. The Abdominal Aortic Tourniquet functions as a large blood pressure cuff which wraps around the lower torso to minimize extremity bleeding.
Limiting or stopping blood flow through the major blood vessel of the body, the aorta, is an established method for slowing the rate of blood loss in a severely injured patient with ongoing bleeding. In the military, this aortic occlusion has traditionally been achieved using a large aortic clamp inserted into the chest cavity via a large incision between the ribs. This dramatic and extremely invasive maneuver is typically a “last ditch” effort. The clamping of the aorta excludes the systemic circulation, by definition, thus causing an ischemia. The goal of the aortic clamping procedure is to keep the patient's remaining blood circulating to the heart, lungs, and brain for precious minutes until bleeding below the aortic clamp is controlled and the patient can be resuscitated and systemic circulation restored. Because of the inherent morbidity of the aortic clamp maneuver, it is often reserved for only the sickest or moribund patients who have lost vital signs and are essentially already dead.
Recently, balloon catheters used in endovascular surgery have been repurposed to fully occlude the aorta by inflation of a balloon in the lumen of the aorta, as an alternative to aortic clamping. This procedure is referred to as Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA). REBOA has the potential to achieve effective aortic occlusion with less morbidity. Therefore, REBOA may be used earlier in the clinical course of the bleeding patient.
As with aortic clamping, REBOA can be used to increase blood pressure to vital organs while slowing ongoing blood loss. However, currently available FDA-approved balloon catheters used for REBOA can only reliably achieve complete occlusion or no occlusion. As such, attempting to wean a patient from complete balloon occlusion by slowly deflating the balloon is not achievable. When aortic occlusion is used in the course of treatment of a hemorrhaging patient, the physician must begin to wean the patient off complete occlusion as early as possible. Using REBOA, when the balloon is inflated, everything below the balloon quickly starts to die due to lack of blood flow. When the balloon is deflated to initiate flow, hemodynamic collapse is a possibility. Additionally, variation in patient size (height, weight, aortic diameter) limits the ability of a single REBOA catheter to effectively occlude aortic flow in all patients.
Currently, REBOA is performed utilizing devices largely intended for other purposes, specifically the FDA-approved CODA® balloon catheter (Cook Medical Technologies, LLC, Bloomington, Ind.) for occluding large blood vessels and molding of aortic endoprostheses. While effective at complete aortic occlusion, the CODA® balloon catheter is not ideally suited for partial vessel occlusion or controlled distal reperfusion during gradual deflation based on its inherent design characteristics, particularly an inability to create a variable and sustained pressure gradient across the balloon. An example of this type of device is disclosed by Eliason et al., U.S. Patent Application Publication No. 2013/0102926, published Apr. 25, 2013, which is incorporated by reference herein in its entirety. The invention of Eliason et al. is directed to a method for placing an aortic occlusion device without having to rely on fluoroscopy to ensure proper placement. The system of Eliason et al. relies on the use of an inflatable balloon to provide occlusion, and thus, has only marginal ability to control variability in flow from upstream to downstream of the occlusion device. Moreover, the system of Eliason et al. is unable to provide controlled anterograde blood flow (i.e., distal reperfusion).
It is well recognized that without controlled distal reperfusion, hemodynamic collapse is common. In particular, hemodynamic collapse has a high probability of occurrence when open aortic cross-clamping is used to staunch blood flow. Although complete occlusion can stop distal blood loss, complete occlusion also causes supraphysiologic blood pressure spikes to everything upstream of the occlusion balloon. These blood pressure spikes can worsen concomitant injuries to tissue beds proximal to the balloon (e.g. traumatic brain injury, pulmonary contusions and hemorrhage, or traumatic amputations of the upper extremities). Additionally, upon uncontrolled release of complete occlusion, the blood volume supplying the heart, lungs, and brain is rapidly redistributed to the lower half of the body effectively reducing the circulating blood volume. Additionally, peripheral vasodilation and the washout of toxic metabolites, which have built up in the ischemic tissues, can result in myocardial suppression and further deterioration of hemodynamics. As a result, the growing clinical experience with REBOA in its current form reveals negative physiologic effects.
The current compliant balloon architecture poses technical challenges for incremental restoration of distal reperfusion necessary to prevent hemodynamic collapse following complete aortic occlusion. As an alternative to compliant balloon architectures, there exist fixed-diameter, non-compliant balloon catheter designs (e.g., ARMADA® by Abbott Laboratories Corp., North Chicago, Ill.). However, these catheters are intended and approved for vessel dilation (angioplasty), typically for narrowed vessels (e.g., atherosclerosis). Additionally, a fixed-diameter, non-compliant balloon catheter must be sized appropriately to properly occlude each patient's aorta. Consequently, although the non-compliant balloon is less susceptible to change in shape due to blood pressure spikes, the inability to change diameter outside of a narrow range impedes its ability to serve as an adaptable device to support both complete occlusion and partial occlusion. Therefore, the relatively fixed diameter of non-compliant balloon catheters limits their real-world applicability across a range of normal aortic diameters.
Other efforts have been directed to development of potential alternative methods of providing aortic occlusion. For example, Barbut et al., U.S. Pat. No. 6,743,196, issued Jun. 1, 2004, describes a plurality of approaches to support aortic occlusion. Each approach described in Barbut et al. includes a catheter having a distally mounted constricting mechanism. Each constrictor is collapsed to facilitate insertion and then expanded once inserted to obstruct blood flow. Barbut et al. describes a constrictor comprising an outer conical shell and an inner conical shell, each having a distal open base and proximal apex. The outer shell further includes a pre-shaped ring to facilitate expansion. Both shells include ports or openings. Flow through the mechanism is controlled by rotating the inner conical shell such that the ports of each shell communicate.
More recently, VanCamp et al, in U.S. Pat. No. 7,927,346, issued Apr. 19, 2011, describes a device to provide temporary partial aortic occlusion to achieve diversion of blood flow to the brain in patients suffering from cerebral ischemia. The primary thrust of the VanCamp et al. invention is the provision of an occlusion device that does not require fluoroscopy to ensure proper placement. VanCamp's device includes an expandable frame with a planar membrane mounted on a first portion of the frame to occlude blood flow. In one embodiment disclosed in VanCamp et al., the membrane includes a fixed size opening in the center of the planar membrane to allow some blood to flow through the opening. Alternatively, VanCamp also discloses that the membrane itself may be somewhat permeable to blood flow to allow some flow. However, VanCamp is unable to provide variable control of blood flow during use.
In light of the aforementioned considerations and limitations of existing and proposed devices, there exists an urgent and unmet need for a viable solution to allow a physician to address hemorrhagic injuries and carefully regulate blood flow, from complete occlusion to sustained partial occlusion, with an ability to adjust the level of occlusion as the patient's vital signs dictate.